JP2018190624A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery arranged so as to be able to suppress the precipitation of a substance originating from a charge carrier, and the voltage drop attributed to self discharge.SOLUTION: A nonaqueous electrolyte secondary battery herein disclosed comprises: an electrode body including positive and negative electrodes; and a nonaqueous electrolyte. The nonaqueous electrolyte contains: a carbonate-based solvent; an ether-based solvent; a supporting electrolyte; and lithium bis(oxalate)borate. The supporting electrolyte is lithium bis(fluorosulfonyl)imide. The concentration of the lithium bis(fluorosulfonyl)imide in the nonaqueous electrolyte is 0.8 mol/L or more and 3 mol/L or less. The weight percentage of the lithium bis(oxalate)borate to the nonaqueous electrolyte is 0.2 mass% or more and 0.4 mass% or less. The mass ratio (Ether-based solvent/Lithium bis(oxalate)borate) of the ether-based solvent to the lithium bis(oxalate)borate is 25 or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used for portable power sources such as personal computers and portable terminals, and vehicle drives such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). It is suitably used for power sources for automobiles.

With the spread of non-aqueous electrolyte secondary batteries, higher performance is desired for non-aqueous electrolyte secondary batteries. For this reason, non-aqueous electrolyte secondary batteries have been developed from various viewpoints. Among them, as an example of development related to a non-aqueous electrolyte, Patent Document 1 discloses a carbonate-based solvent and an ether solvent as a non-aqueous solvent, a supporting salt, and lithium bis (oxalato) borate (Li [B (C ₂ O ₄ ) manufacturing a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte containing ₂ ]). In Patent Document 1, by using such a non-aqueous electrolyte, it is possible to prevent the precipitation of Na [B (C ₂ O ₄ ) ₂ ] on the electrode body due to mixing of a sodium component which is an inevitable impurity. Is described. In Patent Document 1, it is possible to suppress variation in the amount of the coating film formed on the surface of the negative electrode active material due to decomposition of [B (C ₂ O ₄ ) ₂ ] of lithium bis (oxalato) borate. In addition, it is described that an increase in internal resistance when charging / discharging is repeated and that precipitation of a substance derived from a charge carrier (for example, a metal such as metallic lithium) can be suppressed.

JP 2014-053193 A

However, as a result of intensive studies by the present inventor, it has been found that the technique described in Patent Document 1 has room for improvement with respect to suppression of precipitation of substances derived from charge carriers. We also found that there is room for improvement in voltage drop due to self-discharge.
Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery in which the precipitation of substances derived from charge carriers is suppressed and the voltage drop due to self-discharge is suppressed.

  The nonaqueous electrolyte secondary battery disclosed herein includes an electrode body including a positive electrode and a negative electrode, and a nonaqueous electrolyte. The non-aqueous electrolyte contains a carbonate solvent, an ether solvent, a supporting salt, and lithium bis (oxalato) borate (LiBOB). The supporting salt is lithium bis (fluorosulfonyl) imide (LiFSI). The concentration of lithium bis (fluorosulfonyl) imide in the nonaqueous electrolyte is 0.8 mol / L or more and 3 mol / L or less. The weight ratio of lithium bis (oxalato) borate to the nonaqueous electrolyte is 0.2% by mass or more and 0.4% by mass or less. The mass ratio of the ether solvent to the lithium bis (oxalato) borate (ether solvent / lithium bis (oxalato) borate) is 25 or more.

According to such a configuration, when the nonaqueous electrolyte contains a highly polar ether solvent, the solubility of Na [B (C ₂ O ₄ ) ₂ ] in the nonaqueous electrolyte is improved, and Na [B Precipitation of (C ₂ O ₄ ) ₂ ] on the electrode body can be suppressed. Accordingly, the LiBOB-derived film formed on the electrode body can be made uniform, and as a result, the deposition resistance of the substance derived from the charge carrier (metallic lithium in this embodiment) can be improved. On the other hand, when the non-aqueous solvent contains an ether solvent, the polarity of the non-aqueous solvent increases, so that the decomposition of the supporting salt easily proceeds. However, by using LiFSI having a high bond strength as the supporting salt, it is possible to make the decomposition of the supporting salt difficult to proceed even when the non-aqueous solvent contains an ether solvent. Therefore, this can suppress a voltage drop due to self-discharge. The concentration of LiFSI in the non-aqueous electrolyte is in a specific range, the mass ratio of LiBOB to the non-aqueous electrolyte is in a specific range, and the mass ratio of the ether solvent to LiBOB is in the specific range. It is possible to achieve both suppression of the precipitation of the derived substance and suppression of the voltage drop due to self-discharge.

It is sectional drawing which shows typically the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the electrode body used for a lithium ion secondary battery.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that matters other than the matters specifically mentioned in this specification and necessary for the implementation of the present invention (for example, a general configuration and manufacturing process of a nonaqueous electrolyte secondary battery that does not characterize the present invention) Can be understood as a design matter of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in the following drawings, the same code | symbol is attached | subjected and demonstrated to the member and site | part which show | plays the same effect | action. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a so-called storage battery such as a lithium ion secondary battery and a power storage element such as an electric double layer capacitor. Hereinafter, the present invention will be described in detail by taking a lithium ion secondary battery as an example.
It should be noted that the present invention is not intended to be limited to the one described in the embodiment, and the technical idea of the present invention is that other non-aqueous electrolyte secondary batteries provided with other charge carriers (for example, sodium ions). (For example, a sodium ion secondary battery).

  FIG. 1 is a cross-sectional view schematically showing a lithium ion secondary battery 10 according to an embodiment. FIG. 2 is a schematic diagram showing the configuration of the electrode body 40 used in the lithium ion secondary battery 10. As shown in FIG. 1, the lithium ion secondary battery 10 includes a battery case 20 and an electrode body 40 (in FIG. 1, a wound electrode body).

  The battery case 20 includes a case body 21 and a sealing plate 22. The case main body 21 has a box shape having a rectangular opening at one end. Here, the case main body 21 has a bottomed rectangular parallelepiped shape in which one surface corresponding to the upper surface in the normal use state of the lithium ion secondary battery 10 is opened. The sealing plate 22 is a member that closes the opening of the case body 21. The sealing plate 22 is a rectangular plate. The sealing plate 22 is welded to the peripheral edge of the opening of the case body 21 to form a substantially hexahedral battery case 20. The battery case 20 is mainly composed of, for example, a metal material that is lightweight and has good thermal conductivity. Examples of such a metal material include aluminum, stainless steel, nickel-plated steel, and the like. Although a rectangular case is illustrated here, the battery case 20 is not limited to such a shape. For example, the battery case 20 may be a cylindrical case. Further, the battery case 20 may have a bag shape that wraps the electrode body, or may be a so-called laminate type battery case 20.

  In the example shown in FIG. 1, a positive electrode terminal 23 (external terminal) and a negative electrode terminal 24 (external terminal) for external connection are attached to the sealing plate 22. A safety valve 30 and a liquid injection port 32 are formed on the sealing plate 22. The safety valve 30 is configured to release the internal pressure when the internal pressure of the battery case 20 rises to a predetermined level (for example, a set valve opening pressure of about 0.3 MPa to 1.0 MPa) or more. Further, FIG. 1 illustrates a state in which the liquid injection port 32 is sealed with the sealing material 33 after the nonaqueous electrolyte 80 is injected.

  As shown in FIG. 2, the electrode body 40 includes a strip-shaped positive electrode (positive electrode sheet 50), a strip-shaped negative electrode (negative electrode sheet 60), and strip-shaped separators (separators 72 and 74).

  The positive electrode sheet 50 includes a strip-shaped positive electrode current collector foil 51 and a positive electrode active material layer 53. For the positive electrode current collector foil 51, for example, an aluminum foil or the like can be used. On one side of the positive electrode current collector foil 51 in the width direction, an exposed portion 52 is provided along the edge. In the illustrated example, the positive electrode active material layer 53 is formed on both surfaces of the positive electrode current collector foil 51 except for the exposed portion 52 provided on the positive electrode current collector foil 51. However, the positive electrode active material layer 53 may be formed only on one side of the positive electrode current collector foil 51.

The positive electrode active material layer 53 typically includes a positive electrode active material, a conductive material, a binder (binder), and the like. Examples of the positive electrode active material include lithium composite metal oxides such as a layered structure and a spinel structure (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiFePO _4, etc.). As the conductive material, a carbon material such as carbon black (for example, acetylene black or ketjen black) can be adopted. As the binder, various polymer materials such as polyvinylidene fluoride (PVdF) and polyethylene oxide (PEO) can be employed.

  The negative electrode sheet 60 includes a strip-shaped negative electrode current collector foil 61 and a negative electrode active material layer 63. For the negative electrode current collector foil 61, for example, a copper foil or the like can be used. On one side in the width direction of the negative electrode current collector foil 61, an exposed portion 62 is provided along the edge portion. In the illustrated example, the negative electrode active material layer 63 is formed on both surfaces of the negative electrode current collector foil 61 except for the exposed portion 62 provided on the negative electrode current collector foil 61. However, the negative electrode active material layer 63 may be formed only on one side of the negative electrode current collector foil 61.

  The negative electrode active material layer 63 typically includes a negative electrode active material, a binder, a thickener, and the like. As the negative electrode active material, for example, carbon materials such as graphite (natural graphite, artificial graphite) and low crystalline carbon (hard carbon, soft carbon) can be used, and among them, graphite can be preferably used. As the binder, various polymer materials such as styrene butadiene rubber (SBR) can be adopted. As the thickener, various polymer materials such as carboxymethyl cellulose (CMC) can be employed.

  As the separators 72 and 74, for example, a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide can be used. Preferably, a polyolefin resin (eg, PE , PP) is used. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). The separators 72 and 74 may be provided with a heat resistant layer (HRL).

In the electrode body 40, as shown in FIG. 2, the positive electrode sheet 50, the negative electrode sheet 60, and the separators 72 and 74 are wound in order, and the wound electrode body (wound electrode body). 40 has a shape that is flatly pushed and bent along one plane including the winding axis WL. The width b1 of the negative electrode active material layer 63 is slightly wider than the width a1 of the positive electrode active material layer 53. Furthermore, the widths c1 and c2 of the separators 72 and 74 are slightly wider than the width b1 of the negative electrode active material layer 63 (c1, c2>b1> a1). In the example shown in FIG. 2, the exposed portion 52 of the positive electrode current collector foil 51 and the exposed portion 62 of the negative electrode current collector foil 61 are spirally exposed on both sides of the separators 72 and 74, respectively. In the present embodiment, as shown in FIG. 1, the electrode body 40 is formed by gathering the intermediate portions of the positive and negative exposed portions 52 and 62 protruding from the separators 72 and 74, and arranging the positive and negative electrodes disposed inside the battery case 20. The inner terminals 23 and 24 are welded to the tip portions 23a and 24a.
In the present embodiment, the electrode body 40 is configured as a wound electrode body, but may be configured as a stacked electrode body.

  Normally, a sodium component is contained in the lithium ion secondary battery 10 as an inevitable impurity, particularly in at least one of the positive electrode sheet 50 and the negative electrode sheet 60. The sodium (Na) component may exist as sodium alone (typically in an ionic state) or as a compound containing Na as a constituent element.

  In the form shown in FIG. 1, a flat wound electrode body 40 is accommodated in the battery case 20 along one plane including the winding axis WL. The battery case 20 further contains a nonaqueous electrolyte 80. The nonaqueous electrolyte 80 enters the electrode body 40 from both sides in the axial direction of the winding axis WL (see FIG. 2). FIG. 1 does not strictly indicate the amount of the nonaqueous electrolyte 80 injected into the battery case 20.

The non-aqueous electrolyte 80 contains a carbonate solvent and an ether solvent as a non-aqueous solvent.
As the carbonate-based solvent, the same or similar ones used for the nonaqueous electrolyte of a general lithium ion secondary battery can be used. Examples thereof include ethylene carbonate (EC) and propylene carbonate (PC ), Diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), trifluoro Examples thereof include dimethyl carbonate (TFDMC). A carbonate type solvent can be used individually by 1 type or in combination of 2 or more types.
The ether solvent may be the same as or similar to that used for a non-aqueous electrolyte of a general lithium ion secondary battery. Examples thereof include dimethoxyethane (DME), 1,2- Examples include chain ethers such as dimethoxypropane (DMP), and cyclic ethers such as tetrahydrofuran and dioxane. An ether solvent can be used individually by 1 type or in combination of 2 or more types.
When the nonaqueous electrolyte 80 contains an ether solvent that is a highly polar nonaqueous solvent, the solubility of Na [B (C ₂ O ₄ ) ₂ ] in the nonaqueous solvent is increased, and Na [B (C ₂ O ₄ ) ₂ ] can be suppressed. Accordingly, the LiBOB-derived film formed on the electrode body can be made uniform, and as a result, the deposition resistance of the substance derived from the charge carrier (metallic lithium in this embodiment) can be improved.
The proportion of the ether solvent in the non-aqueous solvent is preferably 5% by mass or more, and more preferably 10% by mass or more because the precipitation resistance of the substance derived from the charge carrier (in this embodiment, metallic lithium) is particularly high. 20% by mass or more is more preferable, and 40% by mass or more is most preferable. On the other hand, since the ether solvent has a low flash point, the proportion of the ether solvent in the non-aqueous solvent is preferably 70% by mass or less from the viewpoint of safety.
The non-aqueous solvent may contain a solvent other than the carbonate-based solvent and the ether-based solvent as long as the effects of the present invention are not impaired. Examples thereof include aprotic solvents such as ester solvents, nitrile solvents, sulfone solvents, and lactone solvents.

The nonaqueous electrolyte 80 contains a supporting salt, and lithium bis (fluorosulfonyl) imide (LiFSI) is used as the supporting salt. When the non-aqueous solvent contains an ether solvent, the polarity of the non-aqueous solvent becomes high, so that the decomposition of the supporting salt easily proceeds. However, by using LiFSI having a high bond strength as the supporting salt, it is possible to make the decomposition of the supporting salt difficult to proceed even when the non-aqueous solvent contains an ether solvent. Therefore, this can suppress a voltage drop due to self-discharge.
The concentration of LiFSI in the nonaqueous electrolyte 80 is 0.8 mol / L or more and 3 mol / L or less. When the concentration of LiFSI is less than 0.8 mol / L, the supporting salt becomes insufficient, the ionic conductivity becomes too small, and the battery characteristics are deteriorated. On the other hand, when the LiFSI concentration exceeds 3 mol / L, the amount of decomposition of the supporting salt increases, and the amount of voltage drop due to self-discharge increases.

The nonaqueous electrolyte 80 contains lithium bis (oxalato) borate (LiBOB) as a film forming agent.
The weight ratio of LiBOB to the nonaqueous electrolyte 80 is 0.2% by mass or more and 0.4% by mass or less. When the weight ratio of LiBOB is less than 0.2% by mass, a sufficient amount of film cannot be formed. On the other hand, when the weight ratio of LiBOB exceeds 0.4% by mass, Na [B (C ₂ O ₄ ) ₂ ] is liable to precipitate, and the LiBOB-derived coating film formed on the electrode body becomes non-uniform. As a result, the precipitation resistance of the substance derived from the charge carrier (metallic lithium in this embodiment) is reduced.

In the nonaqueous electrolyte 80, the mass ratio of the ether solvent to LiBOB (ether solvent / LiBOB) is 25 or more. When the mass ratio is less than 25, the effect of suppressing precipitation of Na [B (C ₂ O ₄ ) ₂ ] by the ether solvent cannot be sufficiently obtained, and a substance derived from the charge carrier (in this embodiment, metallic lithium ) Cannot be sufficiently obtained.

  Thus, the concentration of LiFSI in the non-aqueous electrolyte is in a specific range, the mass ratio of LiBOB to the non-aqueous electrolyte is in a specific range, and the mass ratio of the ether solvent to LiBOB is in the specific range. Therefore, it is possible to achieve both suppression of the precipitation of the substance derived from the above and suppression of the voltage drop due to self-discharge.

  In the nonaqueous electrolyte 80, a gas generating agent such as biphenyl (BP), cyclohexylbenzene (CHB), or the like, other than the above-described nonaqueous solvent and supporting salt, unless the effects of the present invention are significantly impaired. Various additives such as a dispersant, a thickener, and the like.

  The lithium ion secondary battery 10 configured as described above can be used for various applications, and preferred applications include an electric vehicle (EV), a hybrid vehicle (HV), a plug-in hybrid vehicle (PHV), and the like. Driving power source mounted on the vehicle. The lithium ion secondary battery 10 can also be used in the form of a battery pack typically formed by connecting a plurality of lithium ion secondary batteries 10 in series and / or in parallel.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

<Production of battery for evaluation>
[Battery No. 1]
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (LNCM) as a positive electrode active material powder, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are LNCM: AB: PVdF = 94: 3: 3 was mixed with NMP to prepare a positive electrode active material layer forming slurry. The slurry was applied in a strip shape on both sides of a long aluminum foil having a thickness of 15 μm, dried, and then pressed to prepare a positive electrode.
Further, spheroidized graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener, C: SBR: CMC = 98: 1: 1 The negative electrode active material layer forming slurry was prepared by mixing with ion exchange water at a mass ratio of The slurry was applied in a strip shape on both sides of a long copper foil having a thickness of 10 μm, dried, and then pressed to prepare a negative electrode.
In addition, two separator sheets (PP / PE / PP three-layer porous polyolefin sheet having a thickness of 20 μm) were prepared.
The produced positive electrode and negative electrode and two prepared separator sheets were superposed and wound to produce a wound electrode body. At this time, a separator was interposed between the positive electrode and the negative electrode.
The produced wound electrode body was accommodated in a rectangular battery case having a liquid inlet.
Subsequently, a non-aqueous electrolyte was injected from the injection port of the battery case, and the injection port was hermetically sealed. 1 lithium ion secondary battery (battery capacity: 5 Ah) was produced.
The nonaqueous electrolyte includes ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and dimethoxyethane (DME), and EC: DMC: EMC: DME = 35: 33: 27: 5. The lithium bis (oxalato) borate (LiBOB) as an additive is added to the non-aqueous solvent contained at a mass ratio of 0.2% by mass with respect to the non-aqueous electrolyte, and the lithium bis (supporting salt) as a supporting salt. What added (fluoro sulfonyl) imide (LiFSI) so that the density | concentration in a non-aqueous electrolyte might be 1.0 mol / L was used.

[Battery No. 2-No. 11]
Except for changing the composition of the non-aqueous electrolyte as shown in Table 1, the battery No. In the same manner as in No. 1, 2-No. 11 lithium ion secondary batteries were produced. In addition, No. 9 and no. In No. 10, LiPF ₆ was used instead of LiFSI as the supporting salt.

<Battery evaluation>
[Limited precipitation resistance]
No. produced above. 1-No. 11 lithium ion secondary batteries were initially charged and then placed in an environment of 25 ° C. to adjust the SOC to 50%. Then, constant current (CC) charging was performed for 500 seconds at a predetermined current value. Then, each lithium ion secondary battery was disassembled, and the presence or absence of deposition of metallic lithium on the negative electrode was confirmed. The maximum current value (C) was calculated | required among the electric current values by which the precipitation of metallic lithium on a negative electrode was not confirmed. The results are shown in Table 1.

[Voltage drop]
No. produced above. 1-No. Eleven lithium ion secondary batteries were initially charged. It was placed in an environment of 25 ° C., and was discharged at a constant current (CC) until it reached 3.0V. Thereafter, it was left to stand for 24 hours for self-discharge, and the voltage drop at this time was measured. The results are shown in Table 1.

From Table 1, No. corresponding to the nonaqueous electrolyte secondary battery according to the present embodiment. 1-No. It can be seen that the lithium ion secondary battery of No. 7 has high limit precipitation resistance (current value of 35 C or more) and a small voltage drop amount during self-discharge (voltage drop amount of 0.050 V or less). No. 1-No. From the comparison of the lithium ion secondary battery of No. 4, it can be seen that the limit precipitation resistance becomes higher as the addition amount of the ether solvent is increased.
On the other hand, no. No. 1 lithium ion secondary battery and No. 1 In comparison with the lithium ion secondary battery of No. ₈ , when a conventional non-aqueous electrolyte in which the non-aqueous solvent does not contain an ether solvent and the supporting salt is LiPF ₆ is used, the limit precipitation resistance is It turns out that it is low.
No. No. 4 lithium ion secondary battery and No. 4 Compared with the lithium ion secondary battery of No. ₉ , when a non-aqueous electrolyte having a supporting salt of LiPF ₆ contains an ether solvent, although the limit precipitation resistance is high, the amount of decomposition of the supporting salt is large. It can be seen that the amount of voltage drop is very large.
No. No. 4 lithium ion secondary battery and No. 4 From comparison with the lithium ion secondary battery of No. 10, it can be seen that when the amount of LiBOB added is too large, Na [B (C ₂ O ₄ ) ₂ ] is precipitated, and as a result, the limit precipitation resistance is lowered.
No. 4-No. No. 7 lithium ion secondary battery and No. 7 From the comparison with the lithium ion secondary battery of No. 11, it can be seen that if the LiFSI concentration is too high, the amount of voltage decrease due to self-discharge increases due to the large amount of decomposition of the supporting salt.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 20 Battery case 21 Case main body 22 Sealing plate 23 Positive electrode terminal 24 Negative electrode terminal 30 Safety valve 32 Injection port 33 Sealing material 40 Winding electrode body 50 Positive electrode sheet 51 Positive electrode current collecting foil 52 Exposed part 53 Positive electrode activity Material layer 60 Negative electrode sheet 61 Negative electrode current collector foil 62 Exposed portion 63 Negative electrode active material layer 72, 74 Separator 80 Nonaqueous electrolyte WL Winding shaft

Claims (1)

A non-aqueous electrolyte secondary battery comprising an electrode body including a positive electrode and a negative electrode, and a non-aqueous electrolyte,
The non-aqueous electrolyte contains a carbonate solvent, an ether solvent, a supporting salt, and lithium bis (oxalato) borate,
The supporting salt is lithium bis (fluorosulfonyl) imide;
The concentration of lithium bis (fluorosulfonyl) imide in the non-aqueous electrolyte is 0.8 mol / L or more and 3 mol / L or less,
The weight ratio of lithium bis (oxalato) borate to the nonaqueous electrolyte is 0.2% by mass or more and 0.4% by mass or less,
The mass ratio of the ether solvent to the lithium bis (oxalato) borate (ether solvent / lithium bis (oxalato) borate) is 25 or more.
Non-aqueous electrolyte secondary battery.

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